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Dental Tribune Middle East & Africa Edition | 3/2016 10 mCME Bioactive materials support proactive dental care mCMEarticlesinDentaltribunehavebeenapprovedby: HaaDashavingeducationalcontentfor2CMECreditHours DHaawardedthisprogramfor2CPDCreditPoints CAPP designates this activity for 2 CE Credits ByJohnC.Comisi,DDS,MAGD Resin bonding of the human denti- tion has become a “standard” in the United States and Canada. There are more than 80 different bonding sys- tems on the market today. We have seen them evolve through multiple generations in an attempt to “sim- plify” the bonding process. Yet, as these agents have simplified, many in our profession have seen many challengesarise. A significant number of reports in the literature have been showing that the “immediate bonding effec- tiveness of contemporary adhesives are quite favorable, regardless of the approach used [however] in the long term, the bonding effective- ness of some adhesives drops dra- matically.”1 The hydrophillicity that both etch-and-rinse and self-etch bonding agents offer initially in the dentin-bonding process becomes a significant disadvantage in terms of longtermdurability.2 It is this hydrophillicity of simplified adhesive systems combined with other operator-induced challenges that contribute to these failures. Tay, Carvalho, Pashley, et al. have reported repeatedly in the literature of this problem.3,4 They continue to report that these bonding agents do not coagulate the plasma proteins in the dentinal fluid enough to re- duce this permeability. The fluid dropletscontributetotheincompat- ibility of these simplified adhesives and dual-/auto-cured composites in direct restorations and the use of resin cements for luting of indirect restorations. The term “water-tree” formation has been coined to describe this process, which originated from the tree-like deterioration patterns that were found within polyethylene in- sulation of underground electrical cables. It is now being applied to the water blisters formed by the transfer of dentinal fluid across the dentin- bonding interface. These “water blis- ters ... act as stress raisers and form initial flaws that cause subsequent catastrophic failure along the adhe- sivecompositeinterfaces.”4 The previously mentioned plasma proteins are released by the dentin when subjected to acids and cause hydrolytic and enzymatic break- down of the dentin and resin bond- ing agent interface.5 These enzymes arecalledmatrixmetalloproteinases (MMPs). Currently, there are only three methods of reducing these MMPs: 2 percent chlorhexidine solutions that are used prior to application of bonding agents; etchants containing benzalkonium chloride, otherwise known as BAC (i.e., Bisco’s Uni-etch products); and polyvinylphospho- nic-acid-producing products (glass ionomer and resin-modified glass ionomers). Due to the short efficacy of these chlorhexidine solutions being used before bonding, this methodology has come into question as of late.6 Etchants with BAC have been shown to be valuable in the reduction of MMPs and should be considered in all bonding pro- cesses.7 However, the most intrigu- ing methodology of reducing MMPs and remineraliz- ing tooth structure is with the use of glass ionomer ce- ments (GIC) and resin-modified glass ionomers (RMGIC). Glassionomers andresin-mod- ifiedglassionomers Glass ionomer cements have long been used as a direct restorative ma- terial.Theirearlyformulationsmade the material difficult to handle, and the breakdown of the material made it an undesirable solution in dental restoration. However, these materi- als, especially in today’s formula- tions and pre-encapsulated presen- tations, have many properties that make them very important in the restorativeprocess. The work at companies such as SDI North America (Riva product line), GC America (Fuji product line) and VOCO (Iono product line) have con- tinued to make great strides in im- proving these products for easier and longer-lasting use of GIC and RMGICproducts. First, these materials are bioactive, and up until recently, they were the only materials with this property; that is they have the capacity to in- teract with living tissue or systems. Glass ionomers release and recharge withionsfromtheoralcavity. This transfer of calcium phosphate, fluoride, strontium and other min- erals into the tooth structure helps the dentition deal with the constant assaultoftheacidicnatureofday-to- day ingestion of food and beverages and encourages remineralization; and the incorporation of phospho- rousintotheacidintoday’sGICscre- atespolyvinylphosphonicacid.8 This property of GICs makes them a majoragentinthereductionofMMP formation, and thereby minimizing ifnoteliminatingthecollagenbreak- down commonly found in many resin-dentinbondingprocedures.9 Second, they bond and ultimately form a union with the dentition by chemicallyfusingtothetooth. The combination of the polyacrylic acid and the calcium fluoroalumino silicate glass typically found in GICs reacts with the tooth surface, which releases calcium and phosphate ions that then combine into the surface layer of the GIC and forms an inter- mediate layer called the “interdiffu- sionzone.”10 No resin bonding agents are re- quiredduetothischemicalfusingto the tooth structure. This ion release helps inhibit plaque formation and provides an acid buffering capability that helps to create a neutralization effect intraorally. In addition, these GICs have very good marginal integ- rity with better cavity-sealing prop- erties, have better internal adaption and resistance to microleakage over extended periods of time, have no free monomers, can be bulk filled and offer excellent biocompatibil- ity.11 Another important consideration is that GICs are moisture-loving ma- terials, which makes them very sen- sible for use in the intraoral cavity. The transfer of dentinal fluid from the tooth to the GIC essentially cre- ates a “self-toughening mechanism of glass ionomer based materials… serves to deflect or blunt any cracks that attempt to propagate through the matrix [and] … plays an adjunc- tive role by obliterating porosities [which]delaythegrowthofinherent cracksintheGICunderloading.”4 The intermediate layer of the GIC provides flexibility during function- al loading and acts as a stress absorb- er at the interface of the restoration andthetooth.12 Resin-modified glass ionomers (RMGIC), which are a hybrid of tradi- tional glass ionomer cements with a small addition of light-curing resin, exhibit properties intermediate of the two materials.13 This material has been shown to have properties simi- lar to GIC, but with better esthetics and immediate light cure. RMGICs have been shown to undergo slight internalfracturingfrompolymeriza- tion shrinkage, yet have an inherent ability to renew broken bonds and reshapetoenforcenewforms.12 Application of RMGIC to all cut den- tin in Class II composite restorations has been shown to “significantly re- duce micro-leakage along (the) axial wall” of the restoration,14 and helps prevent bacterial invasion of the restored tooth. RMGIC biomaterials are multifunctional molecules that can adhere to both tooth structure and composite resin, thus provid- ing an improved sealing ability by chemical or micromechanical adhe- sion to enamel, dentin, cementum andcompositeresin. They, like GICs, can be bulk filled to reduce the amount of composite necessary to restore the cavity prep- aration and act as dentin substitutes intherestoration.15 The use of GIC and RMGIC in the restoration of posterior Class V res- torations and conservative Class I restorationsprovidesmanybenefits. They are easy to place and reasona- blyforgiving,eveninaslightlymoist environment. They should be placed in a moist but not wet environment, so familiarity with technique is im- perative as it is with all dental resto- rations. I will often use Riva SC (SDI) or Fuji 9 GP Extra (GC America) in posterior Class I and V restorations (Figs. 1–7). Polishing and shaping of the mate- rials must be done with water spray and fine/ultra fine composite finish- ing burs and polishers so as not to destroy the surface of the material (Fig.8). The use of RMGIC products, such as Riva LC or Fuji II LC, is great in bicus- pid and anterior Class V restorations, especially in high caries prone pa- tients(Figs.9–12). Class II restorations, however, have always presented a challenge to the clinician. If the operator wanted to use GIC or RMGIC, there was no easy way to do this that appeared to pro- vide satisfactory results. It is with thisinmindthatthe“sandwichtech- nique”wasdeveloped. Itwasthoughtthatusingtheproper- ties of GIC to bond to the tooth and then applying resin-bonding agents and composite to the set GIC could help reduce sensitivity and bond failurestypicallyseeninmanyresin- bondedcomposite(RBC)techniques. Typically, the GIC is placed in the preparation, allowed to set, cut back to ideal form and then bonded to withanRBCtechnique.However,the inability of RBCs to adhere to the set GIC often creates many failures. The materials by themselves are incom- patibleoverthelongterm. The modified sandwich technique evolved as a means to overcome this problem.PlacingRMGICoversetGIC — and then adding a RBC to that — providedabettersolution,butwasas laboriousandtimeconsumingtodo, asisthesandwichtechnique. The‘Co-CureTechnique’ In 2006, an article was published16 that, in my opinion, has revolu- tionized the way I approach direct posterior restorations and direct restorations as a whole. The article presented a radical approach to di- rect posterior restorations, called the Co-CureTechnique.Thistechniqueis defined as the simultaneous photo- polymerizationoftwodifferentlight activated materials that involves “the sequential layering of GIC, RMGIC and composite resin prior to photo-polymerization and be- fore the initial set of the GIC [which] enablesanefficientsingle-visitplace- mentofa[direct]restoration…”16 In the Co-Cure Technique, the com- posite restoration does not require a Fig.1 Fig.2 Fig.3 Fig.4 Fig.6 Fig.11 Fig.5 Fig.7 Fig.12 Fig.10 Fig.9 Fig.8 ÿPage11